The invention relates to gas burners of the type distributing, through multiple nozzles, the flames generated by the combustion of a pressurized fuel gas in air, this gas being for example one or other of the following : natural gas, butane, propane.
Such burners for example equip water heaters, bath heaters, domestic or industrial central heating boilers, cookers, . . .
The invention relates more particularly, among these burners, to those comprising an air-box, an outer wall of which is perforated with a large number of closely spaced orifices, a gas feed-tank connected to a source of pressurized fuel gas, this feed-tank being adapted so as to have, opposite the perforated wall of the air-box, a perforated partition sufficiently distant from said perforated wall for the air to flow freely between said wall and said partition and a plurality of hollow needles each connected sealingly to the edge of a hole of the partition and each opening into the central zone of the inlet of an orifice of the perforated wall so as to define therewith a nozzle for distributing the air-gas fuel mixture forming a flame production site.
In known embodiments of such burners, called "atmospheric" burners, the air-box communicates with the atmosphere and the air used for forming the flame generating fuel mixture is driven through the orifices by the stream of pressurized gas leaving the needle, said orifices having, for this purpose, a profile converging downstream.
It is then difficult to regulate the heating power of the burner over a wide range, because in particular of the need to avoid, for low powers, the extinction of certain flames by return thereof upstream and, for high powers, the extinction of certain flames by detachment thereof downstream.
In addition, the flame generating fuel mixture is not homogeneous, the relative proportion of gas to air being higher in the zone close to the outlet axis of each needle, in which zone the gas stream flows without being hindered by any obstacle, than in the peripheral regions of each distribution nozzle: the result is imperfect combustion of said mixture and the production of undesirable toxic gases, particularly carbon monoxide and nitrogen oxides, in the combustion products.